Impact of two types of time delays and cross-correlated multiplicative and additive noises on stability and stochastic resonance for a metapopulation system

In this paper, we investigate the stability and the shift between the extinction state and the stable one of a large density and the stochastic resonance (SR) for a metapopulation system subjected to two types of time delay terms, cross-correlation noises and multiplicative signal. By using the fast descent method and the method of small delay approximation, the expressions of the effective potential function and the signal-to-noise ratio (SNR) are obtained. We denote by Q the intensity of the multiplicative noise, and M the intensity of the additive noise, θ and τ the two time delay terms introduced into the metapopulation system. Our main results show some facts that time delay θ and the strength of correlation noise λ can restrain the development of the metapopulation, while the other term of time delay τ can accelerate the expansion of the population from the extinction state to the large stable one. We discover that it is possible to enhance the signal-to-noise ratio by adjusting the intensities of the multiplicative, additive noises and the time delays of the stochastic metapopulation system     

Substituted group-directed assembly of six coordination compounds based on pyrazole bifunctional ligands

Six new complexes [Mn₈(μ₄-O)₄(phpz)₈(MeOH)₄]·(MeOH)(H₂O) (1) [Co₂(HphpzH)(Hphpz)₂(phpz)₂]·4(MeOH) (2), Ni(Hphpz)₂ (3), [Ni(Hphpz)₂]·H₂O (4), [Zn₄(pzpy)₄Cl₄] (5) and [Cu₂(pzpy)₂(HCO₂)₂(H₂O)₂] (6) have been synthesized by hydrothermal reactions of MCl₂·4H₂O (M = Mn, Co, Ni, Zn or Cu) with 5-(2-hydroxyphenyl)-3-pyrazole (HphpzH) or 2-(1H-pyrazol-3-yl)pyridine (Hpzpy). The complexes were characterized by elemental analysis, IR spectroscopy and single-crystal X-ray diffraction. Complex 1 is an octanuclear Mn(III) cluster, complexes 2 and 6 are binuclear Co(III) and Cu(II), respectively, complexes 3 and 4 are isomorphous mononuclear species, while complex 5 is a tetranuclear Zn(II) cluster. The magnetic behavior of complex 1 was investigated. Magnetic susceptibility measurements revealed antiferromagnetic exchange interactions between the metal centers in the clusters. The luminescence properties of the complexes were investigated at room temperature in the solid state.     

Realisation of a humidity sensor based on perfect metamaterial absorber

In this paper, we have proposed and investigated a humidity sensor based on perfect metamaterial absorber. The sensor is composed of three layers, which are metallic particle array on the top, porous silicon in the middle layer and metallic film at the bottom. According to the effective medium approximation, the effective permittivity of porous silicon is mainly determined by the filling fraction of water condensation. It is shown that the resonant wavelength displays significant red-shift with the increasing effective permittivity of porous silicon. Furthermore, the simulation results indicate that the refractive index sensitivity of absorber is high to 249 nm/RIU, which makes our structure be an ideal candidate for evaluating the humidity of environment.     

Spin transmutation in (2 + 1) dimensions

We study a relativistic anyon model with a spin-j matter field minimally coupled to an abelian Chem-Simons gauge field with a statistical parameter α. A spin and statistics transmutation is shown in terms of the continuum random walk method. An integer or odd-half-integer part of α can be reabsorbed by change of j. We discuss the equivalence of a large class of Chern-Simons matter models for given j and α.     

Associative versus dissociative adsorption of water on Al(100)

The adsorption of water on Al (100) at 100 K has been studied using Fourier transform infrared-reflection absorption spectroscopy (FTIR-RAS), nuclear reaction analysis (NRA) and work function measurements (Δφ). All results are consistent with molecular adsorption, as no evidence was found for other possible dissociation products such as atomic O or D (H) at this temperature. By condensing alternating layers of D₂O and H₂O, it was found that a narrow feature in the _v(OD) (_v(OH)) region of the spectrum at 2720 cm⁻¹ (3700 cm⁻¹) is associated with non-hydrogen bonded OD (OH) groups in water molecules existing at the ice-vacuum interface. Surface hydroxyl groups resulting from dissociative adsorption exhibit a broader O-D stretch at 2760 cm⁻¹.     

正磷酸铝高压下相变的分子动力学模拟

在300K、-20GPa至40GPa范围内,对正磷酸铝系统进行了定温定压分子动力学模拟.随着压力不断增加,正磷酸铝中的磷氧四面体基本不变,只是各向同性稍有压缩 ;铝氧四面体变得越来越畸变,但铝对氧的配位数仍保持4.所计算的晶胞压缩率与现有实验数据符合良好,晶格常数a比c减少得更厉害.在 20GPa处发生了一级相变,对径向分布函数分析的结果表明,这主要是铝氧四面体中氧 氧位置发生滑移的结果.从高压下回到零压,模拟表明又回复到原来的晶体结构.在 -15GPa下,晶体结构崩溃.对所得结果进行了讨论.     

Homo- and hetero-binuclear ansa-metallocenes of the group 4 transition metals as homogeneous co-catalysts for the polymerisation of ethene and propene

The compounds [M{(CH₂)₄C(η-C₅H₄)₂}(η-C₅H₅)Cl] (M=Zr^*, Hf), [M{(CH₂)₄C(η-C₅H₄)₂}(η-C₅H₅)Me] (M=Zr, Hf), [(η-C₅H₅)MCl₂{(CH₂)₄C(η-C₅H₄)₂}MCl₂(η-C₅H₅)] (M=Zr, Hf), [(η-C₅H₅)ZrCl₂{(CH₂)₄C(η-C₅H₄)(η-C₉H₆)}ZrCl₂(η-C₅H₅)], [(η-C₅H₅)MMe₂{(CH₂)₄C(η-C₅H₄)₂}MMe₂(η-C₅H₅)] (M=Zr, Hf), [(η-C₅H₅)ZrCl₂{(CH₂)₄C(η-C₅H₄)₂}HfCl₂(η-C₅H₅)], [(η-C₅H₅)MCl₂{(CH₂)₄C(η-C₅H₄)₂}Rh(η-C₈H₁₂)] (M=Zr^*, Hf), [(η-C₅H₅)ZrCl₂{(CH₂)₄C(η-C₅H₄)₂}TiCl₃], [(η-C₅H₅)ZrMe₂{(CH₂)₄C(η-C₅H₄)₂}HfMe₂(η-C₅H₅)], [(η-C₅H₅)MMe₂{(CH₂)₄C(η-C₅H₄)₂}Rh(η-C₈H₁₂)] (M=Zr^*, Hf) have been prepared and characterised. ^* indicates the crystal structure has been determined. Their catalytic properties for ethene and propene polymerisation have been explored.     

Radiolytic reductions of Ag(I), Cu(II), Hg(II) and Pb(II) in aqueous-ethanol systems and the effect of colloidal sulfur

Radiation-induced reductions in aqueous AgClO₄, CuCl₂, PbCl₂ and HgCl₂ systems have been measured in the presence of ethanol and for Ag(I) and Cu(II) with several other organic components. In dilute solutions and under deaerated conditions, the rates were consistent with known radical yields and rate constants. Approximately one-third of the radicals formed from ethanol under conditions of complete OH scavenging are ineffective in reducing Cu(II). In the presence of colloidal Cu or Ag, all of the radicals are effective in the reduction. In the presence of 0.4–2 × 10^-3 g-atom 1^-1 of colloidal sulfur, sulfur reduction competes with and augments that of Ag(I) and Cu(II). Ag₂S and CuS are formed with a reaction chain occuring in the Ag system at 1.7 M ethanol. A mechanism is suggested that involves reaction of a radical-cation complex at the sulfur-aqueous interface in which the metal sulfide is formed. HgCl₂ reduction is unaffected by colloidal sulfur and that of PbCl₂ is depressed.     

Modulation of strain,electric field and organic cation rotation on the band gap and electronic structures of organic-inorganic hybrid perovskite CH3NH3PbI3

Band gap modulation engineering is an important step in the application of optoelectronic materials. In this paper, the first-principles calculations were carried out to study the influence of strain, external electric field, spatial orientation of organic cation on the band gaps and electronic structures of organic-inorganic hybrid halide perovskites CH₃NH₃PbI₃. The results show that both the uniform strain and the tetragonal deformation can modulate the band gap obviously. The electric field of 0.2 V/Å is the critical point of the band gap modulation. The band gap increases when an electric field is applied from 0 to 0.2 V/Å. The electric field above 0.2 V/Å will cause the band gap to decrease. The spatial orientation of the organic cation also has modulation influence on the band gap of CH₃NH₃PbI₃, but has no effect on the direct semiconductor characteristics. The above results will be helpful to study the band gap modulation of other organic-inorganic hybrid halide perovskites.